1. Field of the Invention
The present invention relates to a process for preparing .alpha.-alumina fibers, and more particularly to a process for preparing .alpha.-alumina fibers using aluminum nitrate as a starting material.
2. Description of the Prior Art
Since alumina fibers have relatively attractive properties such as a high melting point, high strength, good corrosion resistance, good wear resistance, and light weight, they are very suitable for use as reinforcements for structural materials.
For example, alumina fibers can be added to ceramics, metals or polymers to obtain ceramic matrix composites (CMC), metal matrix composites (MMC) or polymer matrix composites (PMC), as to increase flexibility, strength and high temperature resistance of the matrices.
Alumina fibers have been manufactured by a melt-spinning technique, which is a conventional technique for manufacturing glass fibers. However, since alumina has an extremely high melting point and the melt of it has low viscosity, therefore it is difficult to spin alumina into fibers.
Since the products obtained through application of a sol-gel technique display such characteristics such as high surface area, high strength, and good homogeneity, and the process can be performed at a lower temperature, thereby reducing energy consumption, the process for producing alumina fibers by the sol-gel technique has drawn the interest of many researchers recently.
Blaze in U.S. Pat. No. 3,322,865 discloses a process for manufacturing alumina fibers using aluminum chloride as a starting material. However, problem encountered therein is that the resultant alumina has the disadvantage of being porous since it is difficult to remove the chloride ion. Yogo and Iwahara disclose another process for producing alumina fibers, in which polymerizable organoaluminum compounds are used as the starting materials (J. Mater. Sci., 27, 1499-1504 (1992)). However, synthesis of such organoaluminum starting materials is difficult and costly.